1. Field of the Invention
The invention relates to a process and a device for determining the axial position of two machine spindles.
2. Description of Related Art
One such process, as disclosed in U.S. Pat. No. 5,224,052 to Hamar, includes a laser alignment system having a laser emission element as the optical transmitting device and a photosensitive target as the optical receiving means. With the target, the location of an incident laser beam can be determined. Instead of a tool, the target can be mounted in the shaft of a machine tool, or in a reference part positioned opposite the tool. The laser emission element and the target can be interchangeably mounted on either the reference part or the rotating tool.
In the Hamar patent, it is assumed that both the laser emission element and the photosensitive target are of essentially absolute accuracy, i.e. the smallest measured value which can be displayed by the instrument is relatively great compared to its systematic inherent error. However, this assumption does not always prevail, since although the corresponding measurement devices are to operate with a resolution and accuracy in the micron range, the devices can become inaccurate due to rough treatment and/or strong temperature effects.
It is therefore one object of the present invention to overcome the deficiencies of the prior art and to provide a process which works with high precision together with the pertinent device of the generic type.
Another object of the present invention is to provide a process/device which can not only check itself, but compared to the prior art, can deliver much greater precise measurement results.
Yet another object of the present invention is to provide a process/device which is easy to handle.
Still another object of the present invention is to provide a process/device which is no more expensive than conventional solutions.
The above object, and other objects, are achieved by providing a process for determining the axial position of two machine spindles or shafts relative to one another. The process includes the steps of emitting a light beam from an optical transmitting device mounted on the end face of a first machine spindle wherein the light beam is emitted roughly in an axial direction of the first spindle; providing a flat optical receiving device on an end face of a second machine spindle positioned frontally opposite the first machine spindle to receive the light beam and to determine the light beam""s incidence point in two coordinates; and determining a distance between the transmitting device and the receiving device. The process further includes the steps of moving the first machine spindle into at least three freely selectable, but defined first rotary positions while the second machine spindle is stationary and recording a position of each incidence point of each light spot corresponding to each first rotary position to generate at least three positions. The at least three positions of the incidence point are used to compute the parameters of a pertinent first circle, especially its center point on the optical receiving device or alternatively to specify it in the best possible manner by means of an error compensation method. The process also includes the steps of moving the second machine spindle into at least three, freely selectable, but defined second rotary positions while the first machine spindle is stationary, and recording a position of each incidence point of each light spot corresponding to each second rotary position to generate at least three positions. The at least three positions of the incidence point are used to compute the parameters of a pertinent second circle, especially its center point on the optical receiving device, or alternatively to specify it in the best possible manner by means of an error compensation method. The process also includes the step of computing a parallel offset of the first and second spindles in at least one of a horizontal and a vertical plane from the at least one parameter of the first circle, the at least one parameter of the second circle and the distance between the optical transmitting device and the optical receiving device.
In another embodiment of the invention, the determination of the angular offset (orientation) of two machine spindles or shafts relative to one another is enabled by the implementation of the following process steps: first, the process is carried out as indicated above. Then, the transmitting device and the receiving device are mounted interchanged on the machine spindles or shafts to be studied, so that the optical transmitting device is mounted on the second machine spindle and the optical receiving device is mounted on the first machine spindle. Afterwards the process is repeated analogously as indicated above so that, however, now parameters for the other two, specifically a third and a fourth circle, can be computed. With this data, and considering the distance between the optical transmitting device and the optical receiving device, now the values for the angular offset in the horizontal and vertical direction can also be determined. The computed values for parallel offset and angular offset can be used not only to undertake manual correction of the alignment of spindles, but can also be supplied to an adjustment means which moves at least one of the two spindles to be aligned horizontally and vertically until accurate enough alignment is achieved, whereupon the corresponding spindle can be locked in the conventional manner by means of clamp screws or other fastening devices.
According to the process of the present invention, there is the advantage that a closed circular ring on the target need not be imaged by the laser beam. Rather, it is enough to determine the data of the measurement points on an arc. In especially favorably supported cases, it can be enough to determine the measured values of only three incidence points of the laser beam at a time and to subject the parameters of the circles specified in this way on the receiving device to another computational process. It is especially useful here for the parameters of the pertinent circle to be determined in a direct, noniterative computational process when there are a plurality of acquired measurement points. Here methods of compensation computation are used, especially methods of least squares. In addition to the indicated parameters (x and y position of the center and radius of the circle), therefore, it is also possible to provide details regarding the quality of the compensation results. Thus, important statistical parameters such as relative error, correlation coefficient, skewness of the distribution, etc. can also be given.
The proposed process works essentially without the use of measured inclinometer values. In one version of the invention however there are one or more preferably electronic inclinometers which indicate the actual rotary position of the spindle, and with measurement results which are also used in determining the unknown circles. Thus, determination of the parallel offset and angular offset of the spindle is possible with greater accuracy.
In addition, it is advantageous if all the completed measurements and all pertinent measurement results, optionally also tentative results, are immediately displayed on an electronic screen so that the operator can acquire a subjective impression of the quality of the measurement process.